Medication is often dispensed using a medicine cartridge, such as a glass syringe, having a barrel with a needle at one end and a plunger slidably inserted into the other end and coupled to a rubber stopper. Such cartridges are often referred to as “pre-filled syringes” because they may contain a specific dosage or volume of medication when they are initially provided, as compared to conventional syringes that are furnished empty and filled by the user before making an injection.
The glass syringe and rubber stopper have, for years, provided an ideal drug storage closure having unique properties of impermeability to oxygen, low extractables, biocompability, durability, etc. However, they are both formed by processes that do not lend themselves to tight geometrical tolerances. Tight tolerances were not originally needed by these devices because they were not used mechanically with other devices.
Due to the risk of communicable diseases, a number of syringes and adapters have been developed that are intended to prevent accidental needle sticks and/or inadvertent reuse of a syringe. Conventional passive anti-needle stick safety devices for prefilled syringes must mount to the syringe but not interfere excessively with the force required to move the plunger rod during injection nor prevent the full travel of the plunger rod. The safety mechanism necessarily must be triggered toward the end of the administration of the drug or injection (i.e., near the end of the plunger rod travel). However, since virtually all safety devices locate the syringe against the safety device at a point under the syringe finger flange, the operability of the safety device tends to be dependent on the tolerances of the syringe and stopper.
In addition, because conventional passive anti-needle stick safety devices for prefilled syringes tend to mount to or on the barrel of the syringe, the safety devices tend to obscure the contents of the syringe and must be applied post filling of the syringe.
Prefilled syringes tend to be shipped to pharmaceutical customers as ready-to-fill syringes, which are syringes that have been thoroughly cleaned inside and outside after the forming processes and attachment of a needle have been completed, and then placed in sealed tubs that are then sterilized and shipped to the pharmaceutical customers ready for filling with a medicine. The syringe tubs may contain 100 to 160 syringes, each with a geometrical spacing and access that is consistent with established syringe handling equipment. A safety device applied to the syringe must not obscure the optical inspection systems that are in place to check the syringes prior to filling them with medication.
Accordingly, it would be desirable to have a needle guard for a ready-to-fill syringe having the safety device triggering mechanism independent of the syringe and stopper tolerances, and that assembles to the syringe without adversely affecting the syringe position with respect to the syringe handling tub or the way the handling equipment conveys the syringes during filling and packaging nor impedes the inspection processes.